There are a number of known automotive vehicle safety systems, which are designed to alert the driver of a vehicle if the vehicle is in danger of colliding with a stationary or moving obstacle. Because the collision danger is evaluated based on the speed of the vehicle, such systems are known as vehicle over-speed indicators.
Typically, such safety systems employ a radar device to determine whether there is a danger of a collision with an obstacle in the path of the vehicle. The radar sensor can determine whether the obstacle is in the path of the vehicle, and can also determine the distance from the vehicle to the obstacle and the speed of the obstacle. Typical safety systems further comprise a central processing unit (CPU) programmed to calculate a safe driving speed for the vehicle based on detected obstacles, or a minimum safe distance between the vehicle and such obstacles, based on the location and speed of the obstacles, the maximum deceleration rate of the vehicle (which can be a function of environmental conditions, such as road surface wetness etc), the reaction time of the driver, and the current speed of the vehicle. Examples of such systems can be found in U.S. Pat. Nos. 4,916,450, and 5,931,547.
A simplified block diagram of a conventional active automotive safety system is shown in FIG. 1. A flowchart describing the operating of such an automotive safety system as described is given in FIG. 2. The system incorporates Short Range Radar (SRR) sensors 12 for determining the location and velocity of obstacles 14 in the path of a vehicle 16. Data from these sensors are fed into a CPU 18 (step 30, FIG. 2). Vehicle input devices 20 feed the vehicle characteristics (which might include speed, turning angle, acceleration, traction and detected environmental conditions) into the CPU (step 32, FIG. 2). The CPU collects the data from all the sources and determines if the obstacle is in the path of the vehicle and further determines a safe driving speed of the vehicle (step 34, FIG. 2), or a safe distance between the vehicle and the obstacle. If there is a danger of a collision with the obstacle in the path of the vehicle, due to the speed of the vehicle being in excess of the safe driving speed (step 36, FIG. 2), or due to the distance between the vehicle and the object being less than the minimum safe distance, a warning signal is sent an output device 22 (step 38, FIG. 2). The output device could be, for example, an audio alarm or a visual danger indicator. The warning signal could be accompanied by a system overriding the driver controls to restore safe driving parameters, subject to safety concerns being met.
The safe driving speed calculation method conventionally used is a function of the velocities of the vehicle and the obstacle, and the distance to the obstacle. The reaction time of the driver and the expected deceleration of the vehicle are also factored in to determine a safe driving speed of the vehicle with respect to the obstacle. The driver reaction time is typically estimated by the automotive industry at 2.0 sec.
Typical vehicle safety systems which employ such calculations in determining the danger of a collision with an obstacle in the path of the vehicle, do not normally allow for the fact that the driver's reaction time is not constant.
However, U.S. Pat. No. 5,594,412 discloses a prior art vehicle safety system which determines a minimum safe distance of the vehicle to an obstacle in the path of the vehicle, where the driver reaction time is included in the calculation of the minimum safe distance. The invention disclosed in U.S. Pat. No. 5,594,412 employs an intrusive method to interrogate the driver by means of a device which provides a stimulus to the driver and which measures the resulting reaction time of the driver.
U.S. Pat. No. 5,594,412 has the advantage over other prior art vehicle safety systems in that the variation of the driver reaction time is included in the calculation of the minimum safe distance of the vehicle to an obstacle in the path of the vehicle.
Unfortunately an intrusive method to determine the driver reaction time, such as that disclosed in U.S. Pat. No. 5,594,412, has several drawbacks: firstly a regular driver of a vehicle employing an intrusive method which is regularly repeated to measure the driver reaction time, will tend to ignore the stimulus which is provided for measuring his or her reaction time; secondly an intrusive method is a nuisance to the driver; and thirdly an intrusive method to determine the driver reaction time can be hazardous, for example, if the stimulus is provided to the driver at a time when a critical driver response is required.
A great deal of research has been done to investigate the causes of car accidents (see, for example, “Simple reaction time, duration of driving and sleep deprivation in young versus old automobile drivers”, P. Philip et al., J. Sleep Res. (1999) Vol. 8, Page 9). Apart from the physical and environmental conditions of the car and its surroundings, suggests that driving performance is affected by age, duration of drive, duration of breaks in driving, caffeine intake, etc. The conclusions of that paper are that public awareness, particularly in young drivers, needs to be raised with respect to excessive length of driving.
In a thesis submitted to the faculty of the Virginia Polytechnic and State University, Jun. 3, 2003 by Dennis James Collins and entitled “An examination of driver performance under reduced visibility conditions when using an in-vehicle signing information system (ISIS)”, it is concluded that a system providing the type of information currently found on road signs as an artificial driving aid in an in-vehicle information system is of particular benefit during difficult driving conditions such as in bad weather at night. It is further concluded that such systems are of greater relevant benefit to older drivers compared to younger drivers.
Another example of research is “Reaction time of drivers to road stimuli” by Thomas J Triggs and Walter G Harris, June 1982, ISBN 0 86746 147 0. This paper uses yet another research approach in which the subjects were unobtrusively observed in real world situations rather than being briefed subjects in an experimental situation. The conclusions drawn were that faster drivers have lower reaction times and that certain types of road situation (such a railway level crossing signals and speed detection devices) have the highest response rates for drivers.
It is clear from the range of research referred to above that driver performance is perceived to involve a multiplicity of often conflicting factors. It is for this reason that current automated systems tend to assign a standardised driver reaction time of e.g. 2 seconds or 2.5 seconds.